🛳️ Docker Series: Episode 4 — Dockerfile for Beginners: Build Your Own Container Image

🎬 "Ready to become a Docker chef? In this episode, we’ll write your first Dockerfile — the recipe that creates your own custom container. Simple, step-by-step, with a real app. Let’s cook! 👨‍🍳🍱"

🍳 What is a Dockerfile?

A Dockerfile is like a recipe card for Docker. It tells Docker exactly how to build an image from scratch.

Just like:

• A cake recipe includes ingredients and steps
• A Dockerfile includes base image, dependencies, code, and commands

Once Docker reads the Dockerfile, it builds a Docker image, which you can then run as a container.

👨‍💻 Let's Build Your First Dockerfile

We’ll dockerize a basic Node.js app.

📁 Project Structure:

my-node-app/ ├── Dockerfile ├── package.json └── index.js 

🧠 index.js (your app):

const http = require('http'); const server = http.createServer((req, res) => { res.end('Hello from Docker!'); }); server.listen(3000, () => console.log('Server running on port 3000')); 

📦 package.json:

{ "name": "my-node-app", "version": "1.0.0", "main": "index.js", "scripts": { "start": "node index.js" } } 

🛠️ Writing the Dockerfile

Now create a file called Dockerfile (no extension!) and add this:

# Base image FROM node:18 # Working directory WORKDIR /app # Copy files COPY package*.json ./ # Install dependencies RUN npm install # Copy app source COPY . . # Expose port EXPOSE 3000 # Start the app CMD ["npm", "start"] 

🧪 Build & Run the Docker Image

🔨 Build the image:

docker build -t my-node-app . 

🚀 Run the container:

docker run -d -p 3000:3000 my-node-app 

🌐 Open your browser:

Visit http://localhost:3000 — you’ll see: Hello from Docker!

🧠 What Did We Just Do?

• FROM: Sets the base environment (Node.js)
• WORKDIR: The folder where your code lives inside the container
• COPY: Moves your code into the container
• RUN: Installs dependencies
• EXPOSE: Lets Docker know what port the app uses
• CMD: Tells Docker how to start the app

🛡️ Bonus Tips

• Use .dockerignore to skip node_modules, logs, etc.
• Always pin your base image (node:18 not just node)
• Keep Dockerfiles short, clean, and readable

🎯 Up Next: Docker CLI Mastery

In Episode 5, we’ll explore:

• Most used Docker commands
• How to manage images and containers
• Tricks to make your Docker life easier

💬 Let’s Build Together

Have you written your first Dockerfile? Did it work? Run into any errors?

Comment below — I’m here to help every beginner succeed 🚀

❤️ If you learned something new today, show some love with a like or drop a comment. Share this episode with your Dev.to fam!

🎬 Next: “Docker CLI Cheat Sheet — 15 Commands You’ll Actually Use”